When managing, maintaining and monitoring the performance of an optical network it is important to know the status of individual channels. Switching and recovering operations should be rapidly performed in accordance with a channel status when there is an error in an optical network, as information is transmitted through transmission channels at very high speeds, for example 10 Gbps or more than 10 Gbps. Thus, the status information for each channel should be monitored rapidly, and correctly and in an economical way. Channel monitors and optical spectrum analyzers are well known in the art. Some optical spectrum analyzers are capable of scanning through a series of channels and analyzing a single channel at a time; others, are capable of processing more than one channel at a time. Some spectrum analyzers can be configured to monitor networks of channels and provide information about a wavelength of one or more channels or can be configured to provide information regarding the presence or absence of particular channels.
One spectrum analyzer is described U.S. Pat. No. 5,617,234 issued Apr. 1, 1997 in the name of Koga et al. discloses a multi-wavelength simultaneous monitoring circuit capable of precise discrimination of wavelengths of a wavelength division multiplexed (WDM) signal, and suitable for optical integrated circuits having large resistance to vibration. The device proposed by Koga is an arrayed waveguide grating (AWG) based device having photo detectors coupled to output ports of the AWG. Although Koga's device shares certain similarities with the invention described hereafter, it is believed that this invention provides a low cost spectrum analyzer that requires fewer costly detectors while providing adequate response time.
Since spectrum analyzers can provide varied functionality, it is desired to have one which requires low power, and which is compact and robust.
It is an object of this invention to provide a device for acquiring wavelength information for a plurality of channels having different center wavelengths, and wherein the device requires substantially fewer photo detectors than the number of channels it can resolve.
It is an object of this invention, an optical spectrum analyzer is provided that yields wavelength information about one or more channels simultaneously, or can be used in a more general sense to provide status information regarding the presence or absence of one or more channels from a group of channels.